Docosahexaenoic acid-induced alteration of Thy-1 and CD8 expression on murine splenocytes

Effect of Diet and Exercise on the Peripheral Immune System in Young Balb/c Mice

Although diet and exercise clearly have an influence on immune function, studies are scarce on the effect caused by exercise and the consumption of a carbohydrate-rich or fat-rich diet on the peripheral immune system. The aim of the present study was to evaluate the effect of exercise and the two aforementioned unbalanced diets on young Balb/c mice, especially in relation to BMI, the level of glucose, and the percentage of lymphocyte subpopulations in peripheral blood. The changes found were then related to the synthesis of leptin and adiponectin as well as the production of oxidative stress. The increase in BMI found with the carbohydrate-rich and fat-rich diets showed correlation with the levels of leptin and adiponectin. An increase in leptin and a decrease in adiponectin directly correlated with an increase in total lymphocytes and CD4+ cells and with a decrease in B cells. The increase in leptin also correlated with an increase in CD8+ cells. Glycemia and oxidative stress increased with the two unbalanced diets, negatively affecting the proliferation of total lymphocytes and the percentage of B cells, apparently by causing alterations in proteins through carbonylation. These alterations caused by an unbalanced diet were not modified by moderate exercise.

Maternal diet during pregnancy has tissue-specific effects upon fetal fatty acid composition and alters fetal immune parameters

Both animal and human studies demonstrate that the docosahexaenoic acid (DHA) content of plasma and/or tissue lipids is increased during pregnancy. We hypothesised that increasing the α-linolenic acid (ALA) or longer chain (n-3) PUFA content of the maternal diet during pregnancy influences fetal fatty acid composition and the fetal immune system. Pregnant rats were fed a low-fat (LF) soybean oil diet, or high-fat (HF) soybean, linseed, salmon or sunflower oil diets from conception to 20d gestation. The ALA-rich Linseed-HF diet resulted in an equivalent eicosapentaenoic acid (EPA) status in fetal immune tissues and an equivalent DHA status in the fetal brain to that achieved with the Salmon-HF diet. An (n-3) rich maternal diet during pregnancy associated with the highest expression of CD3 (Salmon-HF) and CD8 (Linseed-HF and Salmon-HF) on fetal thymic CD3(+)CD8(+) cells. The Linseed-HF diet resulted in the highest proportion of CD161(+) cells within the fetal thymus, which correlated with the production of IL-4. These data indicate that dietary ALA supplementation may confer some of the benefits of LC (n-3) PUFA during pregnancy. This should be examined in suitably designed human studies.

Diet-induced docosahexaenoic acid non-raft domains and lymphocyte function

Docosahexaenoic acid (DHA) is an n-3 polyunsaturated fatty acid (PUFA) that generally suppresses the function of T lymphocytes and antigen presenting cells (APCs). An emerging mechanism by which DHA modifies lymphocyte function is through changes in the organization of sphingolipid/cholesterol lipid raft membrane domains. Two contradictory models have been proposed to explain how DHA exerts its effects through changes in raft organization. The biophysical model, developed in model membranes, shows that DHA-containing phospholipids form unique non-raft membrane domains, that are organizationally distinct from lipid rafts, which serve to alter the conformation and/or lateral organization of lymphocyte proteins. In contrast, the cellular model on DHA and rafts shows that DHA suppresses lymphocyte function, in part, by directly incorporating into lipid rafts and altering protein activity. To reconcile opposing biophysical and cellular viewpoints, a major revision to existing models is presented herein. Based largely on quantitative microscopy data, it is proposed that DHA, consumed through the diet, modifies lymphocyte function, in part, through the formation of nanometer scale DHA-rich domains. These nano-scale domains disrupt the optimal raft-dependent clustering of proteins necessary for initial signaling. The data covered in this review highlights the importance of understanding how dietary n-3 PUFAs modify lymphocyte membranes, which is essential toward developing these fatty acids as therapeutic agents for treating inflammatory diseases.

Important differences exist in the dose-response relationship between diet and immune cell fatty acids in humans and rodents

Omega-3 polyunsaturated fatty acids (n-3 PUFA) are noted for their ability to diminish inflammatory and immune responses in vitro and in a variety of animal-based models of autoimmunity and inflammation. Yet, recent systematic reviews suggest that the evidence for these fatty acids having beneficial effects on inflammation or autoimmunity in humans is equivocal. A possible explanation for these disappointing and somewhat paradoxical findings emerged from the analyses described in this review. The available data on the changes in immune cell fatty acid profiles in mice, rats and humans, fed various forms and amounts of n-3 PUFA are summarized and displayed graphically. The dose-response curves generated provide new insights into the relationship between dietary n-3 PUFA and immune cell fatty acid profiles. The author suggests that the poor predictive value of most in vitro as well as many animal trials may, in part, be a consequence of the frequent adoption of experimental conditions that create differences in immune cell fatty acid profiles that far exceed what is possible in free-living humans through dietary intervention. Recommendations for improving the preclinical value of future in vitro and animal-based studies with n-3 PUFA are provided.

Modulation of lipid rafts by Omega-3 fatty acids in inflammation and cancer: implications for use of lipids during nutrition support

Current understanding of biologic membrane structure and function is largely based on the concept of lipid rafts. Lipid rafts are composed primarily of tightly packed, liquid-ordered sphingolipids/cholesterol/saturated phospholipids that float in a sea of more unsaturated and loosely packed, liquid-disordered lipids. Lipid rafts have important clinical implications because many important membrane-signaling proteins are located within the raft regions of the membrane, and alterations in raft structure can alter activity of these signaling proteins. Because rafts are lipid-based, their composition, structure, and function are susceptible to manipulation by dietary components such as omega-3 polyunsaturated fatty acids and by cholesterol depletion. We review how alteration of raft lipids affects the raft/nonraft localization and hence the function of several proteins involved in cell signaling. We focus our discussion of raft-signaling proteins on inflammation and cancer.

Docosahexaenoic acid: membrane properties of a unique fatty acid

Docosahexaenoic acid (DHA) with 22-carbons and 6 double bonds is the extreme example of an omega-3 polyunsaturated fatty acid (PUFA). DHA has strong medical implications since its dietary presence has been positively linked to the prevention of numerous human afflictions including cancer and heart disease. The PUFA, moreover, is essential to neurological function. It is remarkable that one simple molecule has been reported to affect so many seemingly unrelated biological processes. Although details of a molecular mode of action remain elusive, DHA must be acting at a fundamental level common to many tissues that is related to the high degree of conformational flexibility that the multiple double bonds have been identified to confer. One likely target for DHA action is at the cell membrane where the fatty acid is known to readily incorporate into membrane phospholipids. Once esterified into phospholipids DHA has been demonstrated to significantly alter many basic properties of membranes including acyl chain order and "fluidity", phase behavior, elastic compressibility, permeability, fusion, flip-flop and protein activity. It is concluded that DHA's interaction with other membrane lipids, particularly cholesterol, may play a prominent role in modulating the local structure and function of cell membranes.

Synthesis of a novel phosphatidylcholine conjugated to docosahexaenoic acid and methotrexate that inhibits cell proliferation

Here we report the synthesis and characterization of a lipophilic phosphatidylcholine containing the omega-3 fatty acid docosahexaenoic acid (DHA) and the cytotoxic drug methotrexate (MTX). This novel phospholipid combines the fatty acid's and the drug's anticancer activities in a molecule amenable to a liposome bilayer for safe, simultaneous delivery of the two agents. Two phosphatidylcholines were synthesized, from 1-stearoyl or 1-docosahexaenoyl, 2-hydroxy-sn-glycero-3-phosphocholine, to contain MTX in the sn-2 position and either stearic acid or DHA in the sn-1 position. The products contain fatty acid, MTX and phosphorus (1:1:1), and the MTX was released by phospholipase A(2), consistent with the proposed phospholipid structure. The predominant product linked MTX to the glycerol moiety through MTX's gamma-carboxyl group. Liposomes composed of 1-stearoyl, 2-oleoyl phosphatidylcholine plus 1-stearoyl, 2-oleoyl phosphatidylethanolamine and various concentrations of the novel phospholipids caused dose-dependent inhibition of murine leukemia cell proliferation in culture. The DHA- and MTX-containing phosphatidylcholine was more effective than that containing stearic acid, and DHA appeared to synergize with MTX when they were added as free agents or covalently linked in the phospholipid. These data show the feasibility of synthesizing, and the inhibitory activity of phosphatidylcholine with DHA in the sn-1 position and MTX in the sn-2 position, and suggest the compound's potential use in cancer chemotherapy.

Dietary n-3 polyunsaturated fatty acids modulate purified murine T-cell subset activation

Studies in humans and murine disease models have clearly shown dietary fish oil to possess anti-inflammatory properties, apparently mediated by the n-3 polyunsaturated fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). To determine the mechanisms by which dietary EPA and DHA modulate mouse T-cell activation, female C57BL/6 mice were fed diets containing either 2% safflower oil (SAF), 2% fish oil (FO), or a 2% purified EPA/DHA ethyl ester mixture for 14 days. Splenic CD4 T cells ( approximately 90% purity) or CD8 T cells ( approximately 85% purity) were incubated with agonists which act at the plasma membrane receptor level [anti(alpha)-CD3/anti(alpha)-CD28], the intracellular level (PMA/Ionomycin), or at both the receptor and intracellular levels (alphaCD3/PMA). CD4 T cells stimulated with alphaCD3/alphaCD28 or PMA/Ionomycin proliferated and produced principally IL-2 (i.e. a Th1 phenotype), whereas the proliferation of CD4 T cells stimulated with alphaCD3/PMA was apparently driven principally by IL-4 (i.e. a Th2 phenotype). The IL-4 driven proliferation of putative Th2 CD4 cells was enhanced by dietary n-3 fatty acids (P = 0.02). Conversely, IL-2 production by alphaCD3/alpha CD28-stimulated CD4 T cells was reduced in FO-fed animals (P < 0.0001). The alphaCD3/alphaCD28-stimulated CD8 cells cultured from FO-fed animals exhibited a significant decrease (P < 0.05) in proliferation. There were no dietary effects seen in alphaCD3/PMA-stimulated CD8 cells, which produced both IL-2 and IL-4, or in PMA/Ionomycin-stimulated CD8 cells, which produced principally IL-2. These data suggest that dietary n-3 fatty acids down-regulated IL-2 driven CD4 and CD8 activation, while up-regulating the activation of the Th2 CD4 T-cell subset. Thus, the anti-inflammatory effects of n-3 fatty acids may result in both the direct suppression of IL-2-induced Th1 cell activation and the indirect suppression of Th1 cells by the enhanced cross-regulatory function of Th2 cells.

R3230AC rat mammary tumor and dietary long-chain (n-3) fatty acids change immune cell composition and function during mitogen activation

Because anticancer immunity declines progressively with tumor growth, a major focus of current research in tumor immunology is the development of means to stimulate the host immune system. This study determined the effects of dietary long-chain (n-3) fatty acids and tumor burden on immune cell phospholipid composition and membrane-mediated immune defense in rats implanted with the R3230AC mammary adenocarcinoma. Fischer 344 rats (145 +/- 2 g) were fed one of two semipurified diets (20 g/100 g fat) for 21 d before and 17 d after tumor implantation. Diets provided long-chain (n-3) fatty acids at 0 or 50 g/kg of total fat. Mammary tumor growth was 31% lower (P = 0.1) in rats fed long-chain (n-3) fatty acids. Dietary long-chain (n-3) fatty acids had beneficial effects on several host immune defenses, including activation of CD8(+) T cells and type-1 cytokine (interferon-gamma and tumor necrosis factor-alpha) production (P < 0.05). Upregulated immune function in tumor-bearing rats fed the high (n-3) diet occurred concurrently with specific changes in the major membrane phospholipids phosphatidylcholine and phosphatidylethanolamine in high (n-3)-fed rats. Because membrane composition plays a critical role in immune function, additional work is needed to determine the relationship between alterations in the phospholipid composition of immune cells during cancer and subsequent upregulation of host defense in the tumor-bearing state.

Effects of dietary n-3 fatty acids on T cell activation and T cell receptor-mediated signaling in a murine model

A short-term feeding paradigm in mice, with diets enriched with eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), was used to study the modulation of T cell activation via the T cell receptor (TcR) and the downstream pathways of intracellular signaling. Diets enriched in EPA and DHA suppressed antigen-specific delayed hypersensitivity reactions and mitogen-induced proliferation of T cells. Cocultures of accessory cells and T cells from mice given different diets revealed that purified fatty acid ethyl esters acted directly on the T cell, rather than through the accessory cell. The loss of proliferative capacity was accompanied by reductions in interleukin (IL)-2 secretion and IL-2 receptor alpha chain mRNA transcription, suggesting that dietary EPA and DHA act, in part, by interrupting the autocrine IL-2 activation pathway. Dietary EPA and DHA blunted the production of intracellular second messengers, including diacylglycerol and ceramide, following mitogen stimulation in vitro. Dietary effects appear to vary with the agonist employed (i.e., anti-CD3 [TcR], anti-CD28, exogenous IL-2, or phorbol myristate acetate and ionomycin).

Docosahexaenoic acid (DHA) alters the phospholipid molecular species composition of membranous vesicles exfoliated from the surface of a murine leukemia cell line

Previously, we presented evidence that the vesicles routinely exfoliated from the surface of T27A tumor cells arise from vesicle-forming regions of the plasma membrane and possess a set of lateral microdomains distinct from those of the plasma membrane as a whole. We also showed that docosahexaenoic acid (DHA, or 22:6n-3), a fatty acyl chain known to alter microdomain structure in model membranes, also alters the structure and composition of exfoliated vesicles, implying a DHA-induced change in microdomain structure on the cell surface. In this report we show that enrichment of the cells with DHA reverses some of the characteristic differences in composition between the parent plasma membrane and shed microdomain vesicles, but does not alter their phospholipid class composition. In untreated cells, DHA-containing species were found to be a much greater proportion of the total phosphatidylethanolamine (PE) pool than the total phosphatidylcholine (PC) pool in both the plasma membrane and the shed vesicles. After DHA treatment, the proportion of DHA-containing species in the PE and PC pools of the plasma membrane were elevated, and unlike in untreated cells, their proportions were equal in the two pools. In the vesicles shed from DHA-loaded cells, the proportion of DHA-containing species of PE was the same as in the plasma membrane. However, the proportion of DHA-containing species of PC in the vesicles (0.089) was much lower than that found in the plasma membrane (0.194), and was relatively devoid of species with 16-carbon acyl components. These data suggested that DHA-containing species of PC, particularly those having a 16-carbon chain in the sn-1 position, were preferentially retained in the plasma membrane. The data can be interpreted as indicating that DHA induces a restructuring of lateral microdomains on the surface of living cells similar to that predicted by its behavior in model membranes.

Effects of dietary docosahexaenoic acid on surface molecules involved in T cell proliferation

It is known that n-3 polyunsaturated fatty acids (PUFA) such as docosahexaenoic acid (DHA) suppress immunity as compared with n-6 PUFA such as linoleic acid (LA), but the mechanism involved in this phenomenon is still unclear. The present study was designed to assess the effect of dietary DHA on the surface molecules involved in T cell proliferation. Weanling male C57BL/6 mice were divided into four dietary groups that were fed a 10% fat diet for 4 weeks varying in amounts of DHA and LA. As the dietary DHA concentration increased, the surface expression of CD4 and CD8 on splenic T cells decreased, while that of CD28 increased. The surface expression of CD3, however, was invariable in all dietary groups. DNA synthesis of splenic T cells, induced by CD3 crosslinkage with anti-CD3 epsilon monoclonal antibody in the presence of CD28-mediated costimulation, increased as the DHA concentration was elevated. These observations suggest that diets rich in DHA exert some of their immunomodulatory effects by a downregulation of surface expression of CD4 and CD8 and by an upregulation of CD28-mediated costimulatory signal.

Docosahexaenoic acid in phosphatidylcholine mediates cytotoxicity more effectively than other omega-3 and omega-6 fatty acids

We reported previously that docosahexaenoic acid (22:6)-containing phosphatidylcholine (PC), but not oleic acid-containing PC nor 22:6-containing phosphatidylethanolamine, is toxic to tumor cells in vitro. To test whether other polyunsaturated fatty acids share 22:6's cytotoxic activity, we treated cultured T27A murine leukemia cells with PC liposomes composed of stearic acid in the sn-1 position and alpha-linolenic acid (alpha-18:3), arachidonic acid (20:4), or eicosapentaenoic acid (20:5) in the sn-2 position. PC containing 22:6 in both positions was also tested. Following treatment, the cells were monitored for fatty acid composition, liposome uptake and viability. Here we demonstrate that cytotoxicity is unique to 22:6-containing PCs and is not shared by PCs with other polyunsaturated omega-3 and omega-6 fatty acids. Because PCs with fatty acids other than 22:6 were taken up by cells but did not kill the cells, we propose that 22:6-containing PCs incorporated into cellular membranes produce unique changes in the membrane structure incompatible with cell survival. PC liposomes containing 22:6 are potential drug delivery vehicles that may, by virtue of their cytotoxicity, serve concomitantly as adjunct cancer therapy.

The triggering signal dictates the effect of docosahexaenoic acid on lymphocyte function in vitro

Docosahexaenoic acid (DHA) is an n-3 fatty acid beneficial to several human conditions including inflammation and autoimmune disease. To better understand the effect of DHA on immunity, we monitored the rise in cytosolic free calcium, interleukin 2 receptor (IL2R) expression, and proliferation of splenic lymphocytes triggered with three different stimuli in the presence or absence of DHA. We found that 10 microg DHA/mL suppressed concanavalin A-induced mitogenesis and the mixed lymphocyte reaction while concurrently enhancing proliferation stimulated with anti-Thy-1 antibodies. Proliferation, as measured by [3H]thymidine incorporation after 2 to 5 d of culture, was affected by DHA, but earlier activation effects such as elevation of cytosolic free calcium and IL2R expression were not altered. These results imply that DHA incorporated into membrane phospholipids differentially affects the activity of distinct membrane-bound receptors and signaling molecules. This result suggests that DHA may be used to modulate immune responses selectively, e.g., to suppress undesired autoimmunity while maintaining protective immunity.

Docosahexaenoic acid (DHA) alters the structure and composition of membranous vesicles exfoliated from the surface of a murine leukemia cell line

Membrane lipid microdomains are regions of the membrane thought to be functionally important, but which have remained poorly characterized because they have proven to be difficult to isolate. The exfoliation of small membranous vesicles from the cell surface is a continuous and normal activity in many cells. If microdomains are relatively large or stable, they may influence the structure and composition of exfoliated vesicles, which are easy to isolate. We tested the ability of docosahexaenoic acid (DHA), a fatty acid proposed to alter the structure of microdomains, to change the structure and composition of vesicles exfoliated from a murine leukemia cell line. Cells were cultured in normal and DHA-enriched media for 72 h, then washed and given a 15-h exfoliation period. Afterwards, the pooled vesicles and their parent plasma membrane were collected and analyzed. Vesicles and plasma membrane from cells grown in normal culture medium had similar fatty acid compositions, including equal, and low, proportions of DHA, but the vesicles had much more cholesterol and displayed higher anisotropy than the plasma membrane. When cells were grown in DHA-enriched medium, both the plasma membrane and exfoliated vesicles had 10-fold elevated levels of DHA in their phospholipids, with the DHA displacing other polyunsaturates. These cells released vesicles having significantly reduced levels of cholesterol and monoenoic fatty acids than those in normal culture. The anisotropy of these vesicles was also dramatically reduced. These data are consistent with DHA altering the structure and composition of membrane microdomains on the cell surface, and suggest that exfoliated vesicles may prove useful in the further study of membrane microdomains.

Spleen cell survival and proliferation are differentially altered by docosahexaenoic acid

Omega-3 fatty acids have diverse health benefits that are not clearly understood. In this study we have examined the effects of the omega-3 fatty acid docosahexaenoic acid (DHA) on mitogen-activated and resting splenic lymphocytes. DHA inhibited lymphocyte proliferation, producing an apparent block or prolongation of S phase, without evidence for direct cytotoxicity. In contrast, DHA enhanced the survival of resting lymphocytes in culture without inducing cell cycling. When DHA was added at the start of culture, the survival advantage was apparent for 2 to 3 days, after which time typical lymphocyte attrition occurred. Using flow cytometry we observed that both T and B cell recoveries were increased by DHA, but there were DHA dose-dependent alterations of forward- and side-scatter characteristics, with some preference for B cells, perhaps indicating altered membrane properties. Our data imply that DHA may check ongoing immune response while concurrently preserving resting lymphocytes needed for subsequent immune responses.

Docosahexaenoic and eicosapentaenoic acids inhibit in vitro human lymphocyte-endothelial cell adhesion

Dietary supplementation with fish oil, which contains high amounts of long chain omega 3 ((n-3)) polyunsaturated fatty acids (PUFAs), particularly docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), has recently been shown to have protective and ameliorative effects on diseases characterized by chronic inflammatory reactions. Interactions between vascular endothelium, mononuclear cells, and cytokines are crucial steps in the course of inflammatory processes such as chronic graft rejection. We therefore studied the effects of DHA and EPA on both the adhesion of peripheral blood lymphocytes (PBL) to human endothelial cells (EC) in culture and the expression of EC-adhesion molecules and their counterreceptors on PBL. The addition of DHA or EPA to the adhesion assay significantly decreased the adhesion of PBL to untreated EC and tumor necrosis factor-alpha (TNF alpha)-, interleukin (IL) 4-, and lipopolysaccharide-stimulated EC. When EC were pretreated with (n-3) PUFAs for 18 hr, washed, and then stimulated by TNF alpha, IL-4, or lipopolysaccharide, PBL adhesion was also significantly reduced compared with controls. We also showed that PBL preincubated with DHA or EPA, and then washed and chromium radiolabeled, still exhibited an adhesion inhibition to TNF alpha- and IL-4-treated EC as well as untreated EC. Cytofluorometry and immunoenzymatic analyses indicated that pretreatment of EC with (n-3) PUFAs before their activation significantly reduced the EC-induced expression of vascular cell adhesion molecule 1, whereas the level of expression of intercellular adhesion molecule 1 and E-selectin was not modified. Furthermore, we showed that incubation of PBL with DHA or EPA moderately reduced the level of cell surface expression of L-selectin and leukocyte function-associated antigen 1, but not of very late antigen 4. In all cases, the inhibitory effect of (n-3) PUFAs was specific and dose dependent. In addition, DHA seems to be a more potent inhibitor than EPA, but the two compounds in association had an additive effect. Regardless of the mode of action, this inhibitory effect may explain the protective and ameliorative effects of (n-3) PUFAs on diseases involving chronic inflammatory reaction.